Technical Abstract:
Changes in management can convert agriculture from a net source to a net sink of greenhouse gases. A field study was established in 2003 in Indiana on a Typic Haplaquoll to determine the impact of nitrogen management on trace gas emissions. There were five treatments for a corn-soybean rotation implemented: 1) Spring chisel/Fall disk tillage with N fertilizer applied as urea ammonium nitrate (UAN) before planting corn; 2) No-till with UAN applied before corn; 3) No-till with UAN applied to corn in a split application; 4) No-till with winter rye as a cover crop with pre-plant UAN before corn; and 5) Nu-tillage (modified no-till using a nu-till planter) with pre-plant UAN before corn. There were four replicates of each treatment, with both the corn and soybean phases planted each year. Beginning in 2004, gas emissions were measured throughout the growing season. CO2 emissions in corn peaked in late June. Emissions from the chisel-disk and no-till single application systems were similar, with the split fertilizer application, cover crop, and nu-till treatments being slightly lower. For soybeans, CO2 emissions peaked in late July and were higher than corn. The chisel-disk treatment had slightly higher emissions, with the no-till split application and nu-tillage being the lowest. For corn, N2O emissions peaked 4-6 weeks after fertilizer application. Emissions were smallest in the chisel-disk treatment, followed by the split application, the single fertilizer application, nu-till, with the cover crop exhibiting higher emissions, undoubtedly due to the decaying plant material. Soybean, with no fertilizer applications, had lower emissions. The cover crop treatment had the highest rates because of the decaying rye residue. In both corn and soybeans, the treatments served as both source and sink for methane emissions, with the uptake levels being slightly greater over time than emitted levels. Net global warming potentials will be presented.